1. Field of the Invention
The present invention relates to delayed coker unit operations. Specifically, the present invention relates to various seat systems that may be used in conjunction with valves used in a delayed coker unit operation.
2. Background
Petroleum refining operations in which crude oil is processed frequently produce residual oils that have very little value. The value of residual oils can be increased when processed in a delayed coker unit (“DCU”). Residual oil, when processed in a delayed coker, is heated in a furnace to a temperature sufficient to cause destructive distillation in which a substantial portion of the residual oil is converted, or “cracked” to usable hydrocarbon products and the remainder yields a residual petroleum by-product which is pumped into a large vessel hereafter called a “coke drum.”
The production of coke is a batch process. Each delayed coker unit usually contains more than one coke drum. In delayed coking, the feed material is typical residuum from vacuum distillation towers and frequently includes other heavy oils. The feed is heated as it is sent to one of the coke drums. The feed arrives at a coke drum with a temperature ranging from 870 to 910° F. Typical drum overhead pressure ranges from 15 to 35 PSIG. Coker feedstock is deposited as a hot liquid slurry in a coke drum. Under these conditions, cracking proceeds and lighter fractions produced flow out of the top of the coke drum and are sent to a fractionation tower where they are separated into vaporous and liquid products. A solid, residuum called coke is also produced and remains within the drum. When a coke drum is filled, residual oil from the furnace is diverted to another coke drum. When a coke drum is filled to the desired capacity, and after feedstock is diverted to another drum, steam is typically introduced into the drum to strip hydrocarbon vapors off of the solid material. The material remaining in the coke drum cools and is quenched. Solid coke forms as the drum cools and must be removed from the drum so that the drum can be reused. While coke is being cooled in one drum and while the cooled solid coke is being extracted from that drum, a second drum is employed to receive the continuous production of coke feedstock as a part of the delayed coker process. The use of multiple coke drums enables the refinery to operate the furnace and fractionating tower continuously. Drum switching frequency ranges from 10 to 24 hours.
In typical coking operations dramatic heat variances are experienced by elements in the coking operation. For example, a coke drum is filled with incoming byproduct at about 900 degrees Fahrenheit and subsequently cooled after being quenched to nearly ambient temperatures. Not surprisingly, this repetitive thermal cycling may create or cause significant problems including stark heat distributing variances throughout various components of a valve system. The heated residual byproduct utilized in coking operations comes into contact with not only the coke drum, but valve and seat components. This heating and subsequent cooling may result in expansion of various elements within a valve system. As previously mentioned the delayed coking process typically comprises at least two vessels so that while one is being filled the other is being purged of material and prepped to receive another batch of byproduct. Thus, during the off cycle, when a vessel is being purged of its contents it will cool and return to a state of equilibrium. It is this cyclical pattern of dispensing hot residual byproduct into a vessel or through a line and subsequently cooling the byproduct that leads to thermal differential and stress within a vessel, a valve, the valve parts or a line. It is this cyclical loading and unloading and stressing and un-stressing of a vessel, valve or line that is referred to as thermal cycling. Thermal cycling typically results in the weakening or fatiguing of a vessel, a valve and its parts which may lead to a reduction in the useful life of the vessel, valve or line. Advantages of some embodiments include similar seat masses between first and second seats decreasing heat variants. Uneven heat distributions or thermal variants existing between various components of the seat system result in decreased longevity of the constitutive elements of the valve body.